1. Field of the Invention
This invention relates to a high-speed high-pressure puffer type circuit interrupter, and more particularly, it pertains to a pressure system for use in the repetitive adiabatic compression of the interrupting gas, such as for instance, sulfur hexafluoride (SF.sub.6).
2. Description of the Prior Art
The puffer concept has been used in the past for power circuit breakers principally as a cheap and simple substitute for a two-pressure system at relatively moderate ratings. Recently it has been demonstrated that puffers can be extended to unexpectedly high ratings. Heretofore it had not been anticipated that a buffer could be superior to a conventional two-pressure breaker in certain respects.
Generally, a high pressure of an arc extinguishing gas such as SF.sub.6 is necessary because the higher the pressure the quicker the arc extinction. However, attempting to store SF.sub.6 at high pressures causes liquefaction at lower temperatures. Prior attempts to heat SF.sub.6 to prevent liquefaction have proven costly. Accordingly, the base pressure of SF.sub.6 gas in a puffer is usually maintained no higher than approximately 70 psi in order to avoid the necessity for heaters. Since the interruption capability of the breaker increases with pressure differential, it is desirable to create as high an upstream pressure as possible, for instance, as high as 600-800 psi.
In the conventional two-pressure system the upstream pressure is limited by practical considerations of the heaters to approximately 225 psig. In the puffer there is no such limitation since the gas is compressed adiabatically. There are some practical upper limits to adiabatic compression since the interrupting pressure must be developed in approximately 10 milliseconds for a two-cycle breaker. Energy to produce the compression for several consecutive operations must be stored in the device somewhere. Pressures above 800-1000 psi become non-competitive from a pressure vessel code point of view.